We describe an optical detection technique that delivers high signal-to-noise discrimination to enable a multi-parameter flow cytometer that combines high performance, robustness, compactness and low cost. The enabling technique is termed “spatially modulated detection” and generates a time-dependent signal as a continuously fluorescing (bio-) particle traverses an optical transmission pattern along the fluidic channel. Correlating the detected signal with the expected transmission pattern achieves high discrimination of the particle signal from background noise. Additionally, the particle speed and its fluorescence emission characteristics are deduced from the correlation analysis. Our method uses a large excitation/emission volume along the fluidic channel in order to increase the total flux of fluorescence light that originates from a particle while requiring minimal optical alignment. Despite the large excitation/detection volume (~ 1mm), the mask pattern enables a high spatial resolution in the micron range. This allows for detection and characterization of particles with a separation (in flow direction) comparable to the dimension of individual particles. In addition, the concept is intrinsically tolerant of non-encoded background fluorescence originating from fluorescent components in solution, fluorescing components of the chamber and contaminants on its surface. The optical detection technique is illustrated with experimental results on multi-color detection with a single large area detector by filtering fluorescence emission of different particles through a patterned color mask. Thereby the particles’ fluorescence emission spectrum is encoded in a time dependent intensity signal and color information can be extracted from the correlation analysis. The multicolor detection technique is demonstrated by differentiation of micro-beads loaded with PE and PE-Cy5 that are excited at 532 nm.

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This paper presents the design and implementat i o n (using a T I 9900 microcomputer system) of digi t a l control systems f o r an environmental chamber u t i l i z e d i n the study of plant growth. Two control systems were implemented -one t o control dry-bulb temperature and the other t o control t h e carbon dioxide content i n the chamber atmosphere. I n add i t i o n , real-time data a c q u i s i t i o n , automatic r es t a r t following power outages, and an i n t e r a c t i v e operating system have been achieved.The CO system i s a closed-loop modified proportional control system. The closed-loop tempera t u r e control system uti1 ized a proportional-plusintegral-plus-derivative d i g i t a l c o n t r o l l e r . The environmental chamber i s presently used i n research by t h e USDA a t A u b u r n University. 2 Thi s paper presents the design and imp1 ementat i o n of a d i g i t a l control system f o r an environmental chamber designed f o r the study of plant growth [ l ] . Two control systems were implementedone t o control dry-bulb temperature and the other t o control t h e carbon dioxide (CO2) content in t h e chamber atmosphere.The chamber i s constructed of plexiglass with measurerrients of approximately 0.7 x 1 . 3 x 2 meters.The chamber system i s hermetically sealed such t h a t both moisture content and carbon dioxide content can be accurately monitored.The hardware i n t h e temperature control system will be described f i r s t . The chamber i s cooled ( a i r conditioned) t o t h e extent t h a t heaters a r e required t o maintain the desired temperature. T h u s t h e heaters a r e the c o n t r o l l i n g elements in t h e closed-loop system. A temperature sensor t h a t has an output in t h e m i l l i v o l t range i s used. The temperature signal i s amplified and applied, t h r o u g h an A/D converter, t o a Texas Instruments TMS 9900 microcomputer system. The measured temperature i s then subtracted from the desired temperature, which i s stored i n the microcomputer. Next t h i s e r r o r signal i s processed by the TMS 9900 ( t h e system compensation), r e s u l t i n g in an output signal t o t h e heater i n t e r f a c e . The heater i n t e r f a c e i s a complex logic c i r c u i t [ l ] which converts the computer outp u t signal i n t o t r i a c s [ Z ] control pulses. The t r i a c s control the e l e c t r i c a l energy i n t o the heate r s by i n e f f e c t c o n t r o l l i n g the rms voltage applied to the heaters. The hardware description of t h e CO2 control system i s given next. The CO2 content of the chamber atmosphere i s measured by the gas analyzer i n p a r t per million (PPM). This signal i s compared t o t h e desired s e t p o i n t , and i f the e r r o r i s negative (a CO2 d e f i c i t ) , the computer opens a solenoid valve from a CO2 supply f o r a length of time depend e n t on che-error magnitude. The control system has no c a p a b i l i t y t o remove excess CO2. Because of the time lag required f o r the gas a n a l y s i s , ...

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